@helpscout/helix/docs/guides/create-spec.md

A Faker-powered fixture generator for Javascript

# Creating a Spec

Let's get started in creating a [Helix spec](../api/HelixSpec)!

Using the `createSpec` function, we'll pass in the shape of our spec with the appropriate [Faker methods](https://github.com/marak/Faker.js/#api-methods).

Note: Helix slightly enhances Faker, but the methods remain the same! Check out **[Faker's API methods](https://github.com/marak/Faker.js/#api-methods)** for a complete list.

## Creating a Spec

Let's create a `Dinosaur` 🦎

```js
const Dinosaur = createSpec({
  id: faker.datatype.number(),
  name: faker.name.firstName(),
  location: faker.address.country(),
});
```

Perfect! Just like that, we've defined our `Dinosaur` (Dino DNA!). However, if you `console.log` it, you'll noticed that it doesn't actually have any fixture data (yet).

```js
console.log(Dinosaur);
// { id: [Function], name: [Function], location: [Function] }
```

The default Faker methods would have rendered some nice fixture data for you the moment you instantiate the methods. However, Helix's `faker` does not!

The actually render the fixture data, we'll need to generate it.

## Single-value Specs

You can also create a HelixSpec which generates a single value. For example, if you have a data type `DinoType` with a set of constant values, you can create a spec to capture this like so:

```js
const DinoType = createSpec(
  faker.random.arrayElement([
    "tyrannosaurus-rex",
    "velocirapter",
    "stegosaurus",
  ])
);

const Dinosaur = createSpec({
  id: faker.datatype.number(),
  name: faker.name.firstName(),
  location: faker.address.country(),
  type: DinoType,
});
```

## Generating fixture data

To generate the fixture data, use the `.generate()` method on your Spec. This returns a regular object in the shape of your Spec.

```js
Dinosaur.generate();
// {
//   id: 1231,
//   name: 'Alice',
//   location: 'Canada'
// }
```

Because of how Faker works, you'll get a different result every time you `generate()`

```js
Dinosaur.generate();
// {
//   id: 1231,
//   name: 'Alice',
//   location: 'Canada'
// }

Dinosaur.generate();
// {
//   id: 5573213,
//   name: 'Tim',
//   location: 'Japan'
// }
```

To keep your fixture, you can cache it as a regular JS variable:

```js
const myDanosawur = Dinosaur.generate();
// {
//   id: 1231,
//   name: 'Alice',
//   location: 'Canada'
// }

// myDanosawr.name will always be Alice!
```

And that's it! You've generated some fixture data for your Dinosaur.

## Up next

Learn how to generate consistent fixture results by **[seeding](./seeding.md)**.